Plastic storage bags having zipper-type closures are known in the art and generally provide adequate closing function; but there is a risk of leaking where the far left side of the zipper and the far right side of the zipper intersect the left and right side edges of the bag. One approach to address these leaking concerns has been to ultrasonically weld the zipper profiles prior to heat welding for side sealing of the overall edge. This approach is based on a thinking that the heat welding alone used for the side sealing has insufficient sealing capacity to seal the zipper profiles, which are much thicker than the side walls away from the zipper profiles. The ultrasonic welding of the zipper profiles at the bag edges involves pressing the profiles together and vibrating with ultrasonic energy. The resulting vibration friction generates heat which melts the plastic so that it welds together. There is a continued desire and need to improve on this and other designs.